Human monocytes are normal cells with numerous functions which have potential roles for preventing new tumors or eradicating established malignancies. Studies have been performed which have allowed us to establish a group of highly immunologically-characterized normal human donors which are part of a longitudinal analysis of normal human monocyte function and other components of the immune response. Investigations have particularly focused on the potential antitumor functions of normal human monocytes. We have been able to isolate large numbers of sterile human monocytes by elutriation and subsequently cryopreserve them in suspension. We have studied the spontaneous cytotoxicity of monocytes to a wide range of tumors and how this function is up-regulated by macrophage activating factors. We developed methodology for separating human monocytes into subsets by size and density and we are testing these subsets for distinct differences in tumor cytotoxicity and BRM release. We have isolated a gene library from activated human monocytes and we have transfected this library into bacteria in preparation for analyzing the function of cells that have been genetically engineered with human monocyte genes.